I have a suspicion that leaving A-Trac on affects MPGs. I noticed this on my '09, but never had any long-term data to verify. On my 2010, I've been keeping track of MPGs on every tank of gas. On only three tanks of gas have I gotten less than 17 miles to the gallon, and this includes lots of towing and hauling and 4wd use. I've also kept driving style and tire pressure fairly consistent.

On the attached chart, you can see the three tanks. For each of these, I had depressed A-Trac for one reason or another and forgot to turn it off.

The A-TRAC isn't on when you are not in L4. It only comes on in L4 when there is a loss of traction. You can hear it when it is on! I call it a grawling sound.

Just like when in 4WD, there is an A-TRAC light that comes on (along with the VSC OFF and ABS OFF lights). There is nothing A-TRAC does to alter mileage when it is on in L4... In fact, by preventing the free spinning of non-traction tires, it would save you gas... However, in Low Range 4WD... your mileage isn't the best, naturally.

Traction control (TRAC, AUTO LSD, A-TRAC) limits or nearly stops a non traction tire from spinning freely so the opposite tire gets the torque to keep you going... the degree of limited slip with Traction Control depends on the drive mode you are in.

2) AUTO LSD (in H2) and TRAC in H4 both have a higher level of limited slip, very effective... like Posi-Traction. Those without A-TRAC can perform the yellow wire mod to have '4-Lo TRAC' and find it quite a bit of an improvement over the normally open differentials in L4.

3) A-TRAC (Active Traction Control) is a strong, 'locker-like' limited slip system that nearly matches wheel rotation across the axle on both the front and back. Available only on Off Road 4WD Tacomas from 2009+ which are equipped with a hydraulic brake booster (vs. the vacuum brake booster on the other Tacoma models).

And TRAC works through engine regulation, right? So maybe that's what I've experienced affecting my MPGs.

Click to expand...

no, trac works by applying brakes to a spinning wheel to transfer power to the other wheel on each axle... (ex. front left spins, brakes are applied and power is transferred to the front right wheel)

what is the mpg that you are getting and what are you towing. naturally towing is going to kill mpgs. Also, what are you using 4wd for. typically when you are in 4wd you wouldnt be watching mpg. my mpg sucks when offroading in 4wd...

When towing our 19' Bayliner, my mileage is usually in the low 17s. Same with our tent trailer, although I did get 20.1 pulling it from Santa Barbara one time. Yes, I drive like an old man.

After a day of wheeling and highway driving last Saturday, my tank averaged 18.9.

The three drops on my chart are regular driving (no towing, no 4wd, consistent tire pressure) with the A-Trac button depressed. I'm not sure what else to control for or what would cause my mileage to drop by 2 MPGs for the tank average.

2) A-TRAC uses sensors that monitor wheel rotation and when activated in L4 only, it is on standby to brake any non-traction tire to match rotation of the traction tire. In the same manner as TRAC and AUTO LSD does, but much stronger braking/ torque transfer... why it only works in L4 which limits your speed to crawling with maximum power.

My A-TRAC button was pushed once... months ago, and never again. Anytime I go into L4, the A-TRAC is on automatically... the way it should be for maximum traction. A second push of the A-TRAC button de-activates it, if for some reason you want torque only going to non-traction tires... open differentials.

The same when you go into H4, the TRAC is on automatically for maximum traction in high range. If you want to have open differentials without limited slip, then stop and hold in the VSC OFF button for a few seconds until the lights indicate it is off (VSC and TRAC work together... and are both off together).

A-TRAC is a seperate animal, requires a hydraulic brake booster, does not work with VSC or ABS (they are both off).

So, you can push the A-TRAC button when you go into L4, and A-TRAC is on stand-by waiting for you to lose traction... so it doesn't even operate with the button pushed until it is needed... and you will hear it when it is working!

As soon as you go into H4 or H2, the A-TRAC no longer is on standby, since it cannot operate out of Low Range. No need to push the button to 'turn it off' when you are not in L4... since it cannot come on.

A note on the rear locking differential... with A-TRAC available, it is no longer needed unless you want to drive out of a stuck with it (as it is only for emergency use per Toyota)... But, you shouldn't be stuck with the A-TRAC on! The A-TRAC makes noise... and the rear locker doesn't... but without A-TRAC your front is an open differential and with A-TRAC you have the traction ability of front and rear lockers, without the steering problems or 5 mph speed restriction (per Toyota).

I am glad the rear locker is still on the A-TRAC truck, better to have it and not need it... then to need it and not have it... Also, until buyers learn how great A-TRAC is, the rear locker helps sell trucks. I know I wouldn't get my 2010 without it... and it took me some time and help here to learn what A-TRAC was! It blows you away, I have learned!

I can assure the button does nothing except when you are in L4. The Taco has TRAC in H4 and H2. Maybe you should turn off TRAC (VSC OFF MODE) if you think traction control reduces mileage? There are not two traction controls running at the same time... and as I said before, the A-TRAC lets you know when it is operating by the noise. That noise only happens in L4 with a loss of traction... Anyway, having more traction is better for gas mileage... spinning tires waste gas, afterall.

However, I have no reason to not play along and push the button when I am not in L4. Now, since it isn't even in the circuit... pushing it when I am not in L4 does nothing... So, I will go into L4, turn off A-TRAC, go back into H2 and continue to monitor my mileage. I just filled up yesterday at the half tank point on the gauge (9 gallons).